Brush assembly for a slip ring

ABSTRACT

A slip ring, mounted on a rotating shaft, is contacted by four pairs of spring loaded, pressure activated, gas cooled brushes. The brush assembly is supported in one-half of a seal housing, the other half of which provides conventional shaft sealing. The housing for the brush assembly is an annulus having end walls and inner and outer peripheral walls, the inner peripheral wall surrounding the ring and having a plurality of circumferentially spaced openings. The brush assemblies are mounted within the housing and are driven through the apertures into contact with the ring. The brushes are supported from the ends of a leaf spring, the center of which is in turn supported by a support spring which is gas pressure actuated.

United States Patent 1 Twarog, Jr.

[11] 3,826,942 July 30, 1974 BRUSH ASSEMBLY FOR A SLIP RING [73]Assignee: Avco Corporation, Stratford, Conn.

[22] Filed: Oct. 25, 1972 [21] Appl. No.: 300,445

3,278,777 10/1966 Grooms 310/240 Primary Examiner-R. Skudy Attorney,Agent, or Firm-Charles M. Hogan; lrwin P. Garfinkle [5 7 ABSTRACT A slipring, mounted on a rotating shaft, is contacted by four pairs of springloaded, pressure activated, gas cooled brushes. The brush assembly issupported in one-half of a seal housing, the other half of whichprovides conventional shaft sealing. The housing for the brush assemblyis an annulus having end walls and inner and outer peripheral walls, theinner peripheral wall surrounding the ring and having a plurality ofcircumferentially spaced openings. The brush assemblies are mountedwithin the housing and are driven through the apertures into contactwith the ring. The brushes are supported from the ends of a leaf spring,the center of which is in turn supported by a support spring which isgas pressure actuated.

7 Claims, 3 Drawing Figures 1 BRUSH ASSEMBLY FOR A SLIP RING BACKGROUNDThe use of slip rings for transferring electrical energy betweenrotating and stationary components is very old, but most applicationshave been limited to relatively low speeds. Recent developments haveresulted in significant improvements and some slip rings used in gasturbine engines satisfactorily transmit signals in the order ofmillivolts at shaft speeds as high as 100,000 r.p.m. with contactvelocities of 6,5000 feet per minute. Certain of these slip rings havehad life expectancies ranging from 5 to 50 hours of use.

The present invention seeks to improve the prior art slip ring bypermitting operation with contact velocities up to 20,000 feet perminute with improved life expectancies. In addition, this inventionimproves the prior art by positioning a pair of slip rings in one-halfof the housing of a conventional engine seal so that the sealingfunction and the slip ring function are simultaneously accommodated.

In order to obtain good signal transfer over a period of time and avariety of speeds, general slip ring requirements are as follows:

l. Low electrical resistance variations due to'rubbing contact.

2. Low electrical resistance variations due to brush bounce.

3. Low wear of rubbing components.

4. Limitation of heat generation to prevent destruction of contactmaterials.

5. Elimination of loose material generated by rubbing cont-act.

6. Protection from foreign material.

This invention improves the prior art slip rings and meets all of theforegoing requirements. These results are accomplished by mounting thecontacting brushes in pairs, four pairs being used around the peripheryof the ring. The pairs are spring loaded and are piston operated inresponse to air pressure so that the brushes are in running contact withthe ring only when signals are being transferred. The system alsoprovides gas flow cooling and cleaning, thus further reducing wear.

THE DRAWINGS For a better understanding of the precise nature of thisinvention reference should now be made to the attached drawings inwhich:

FIG. 1 is an end view, partly in section, of a preferred embodiment ofthis invention;

FIG. 2 is a section taken through the line 2-2 of FIG. 1; and

FIG. 3 is a section taken through the line 3--3 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The slip rings provided inaccordance with this invention are supported within one-half of aconventional seal housing normally used for sealing a rotating shaft 11.The spring loaded carbon seal 12 is conventional and, as shown in FIGS.2 and 3, occupies the right half of the seal housing 10. The remainderof the housing 10 is occupied by two sets of slip ring assemblies.Although two such assemblies are shown, any number capable ofaccommodation by the housing l0 \M; may be 'iis'ed. Since the slip ringassemblies are identical, only one is described.

Each of the two slip rings assemblies includes a conducting ring 13imbedded in a non-conducting insert 14 on the shaft 11. The conductingrings 13 are each electrically connected by means of a lead 15 to asignal source (not shown) such as a strain gage or other sensor securedto the shaft.

Each ring 13 is contacted by a set of four identical brush assemblies 17mounted in the housing 10 and spaced from the seal 12 between insulatingdisc spacers 16. Each of the brush assemblies 17 consists of twospring-loaded brushes l8 and 19 which are electrically interconnected bya leaf spring 20. The assemblies 17 also include a brush lifting andactuating spring 22 connected to the spring 20 by a piston 24. Anelectrical connection to the brushes is made through the piston 24 and alead 26.

The brush lifting and actuating spring 22 provides the support for thebrushes l8 and 19 and in addition transmits the contacting forces to thebrushes. It is supported within the housing between adjacent inletmanifolds 28 positioned apart within the housing, and each spring 22extends axially between the spacers 16. The space between the outerperiphery of the housing 10, the spring 22, and the spacers 16 providesan annular chamber 27 into which pressurized air is admitted foractuating the spring.

The housing 10 has an inner peripheral wall 29 around which the brushassemblies are located. The wall 29 is provided with two sets ofapertures. Apertures 30 permit the radial travel of the brushes from anon-contacting position into a ring contacting position. Apertures 31provide a gas inlet to the surface of the rings 13. Air of freonsupplied to the inlet manifolds 28 is directed through ports 32 in themanifold and through aperture 31 onto the surface of the respective ring13 for cooling and cleaning the rings and brushes.

Normally the brushes l8 and 19 are biased out of contact with theirassociated ring 13 by the spring action of spring 22 and are driven intocontact with the ring by admitting brush actuating air under pressure tothe chamber 27 via a valve 34 and an airinlet 36. The pressurized airserves to apply gas pressure to all of the brush actuating springs 22thereby driving the" springs 22, along with the attached pistons 24 andbrush supporting leaf springs 20, radially inward. This action drivesthe brushes l8 and 19, through the apertures 30, into contact with anassociated ring. Since the leaf springs 20 and the associated pistons 24travel to a positive stop against the inner peripheral wall 29, thecontact pressure of the brushes against the ring 13 is determined solelyby the amount of prestressing of leaf spring 20.

SUMMARY In summary, two sets of slip ring assemblies are installed inthe housing 10 of conventional carbon seals in the position normallyoccupied by one of the seals. Four brush-segment assemblies per set areused with two brushes l8 and 19 per assembly 17. Thus 8 brushes contacteach ring 13, and this redundancy of brush contacts substantiallyeliminates contact resistance variations on the rings. The use of dualcontacts per assembly insures efficiency of contact by providing anout-ofphase brush vibration frequency. Brush and ring wear is reduced toa minimum by the brush lifting springs 22 which hold the brushes 18 and19 out of contact with rings 13 when the assembly is not activated byair pressure. All brushes l8 and 19 are actuated into contact with therings 13 by pressurizing the annular chamber 27 above the brush liftingspring 22 which deflects to a positive stop. With the springs 22 and 20bottomed, a high natural frequency is attained since the assembly massis reduced to the mass of the brushes 18 and 19 and leaf spring 20.Initial brush contact pressure is predetermined by fixing the allowableleaf spring deflection. Brush cooling is accomplished by air leakagepast the support springs 22, and by the admission of pressurized air orfreon channeled to the four manifolds 28 which direct flow to the sliprings 13.

The brushes l8 and 19 are driven into contact with the rings 13 onlywhen it is desired to make a reading ser number may be used depending onthe system requirements. Furthermore, the slip ring need not be used incombination with the seals but may be used separately, or the particularembodiment may be readily modified to add additional rings andassociated brush assemblies.

I claim:

1. A slip ring assembly for providing an electrical connection to aconductive ring fixedly mounted on the periphery of a rotating shaft,the combination comprismg:

a stationary annular housing having axially spaced end walls and outerand inner peripheral walls, said housing being coaxial with said shaft,said inner wall surrounding said conductive ring and being spacedtherefrom, and having a plurality of circumferentially spaced openings;

4 a plurality of radially displaceable circumferentially extending leafsprings supported within said housmg; 4 first and second electricallyconductive contact brushes mounted on the respective ends of said leafsprings; and

means for radially driving said leaf spring toward said axis to driveeach of said brushes through said openings and into contact with saidring.

2. The invention as defined in claim 1 and a support for each of saidleaf springs, said support comprising a plurality of relatively heavysupport springs extending circumferentially within said housing, theends of said support springs being fixed, the spaces between saidsupport springs and the outer peripheral wall of said housing defining achamber, the center of said support spring being connected to the centerof said leaf spring, said support spring being radially inwardlydeflectable to deflect said leaf spring and drive said brushes intocontact with said ring.

3. The invention as defined in claim 2 wherein said means for deflectingsaid leaf spring comprises means for admitting gas under pressure tosaid chamber for radially deflecting said support spring.

4. The invention as defined in claim 3 and a plurality of gas inletmanifolds in said housing, the ends of said support springs being fixedagainst said manifolds, and gas passageways through said manifold andsaid inner peripheral wall to admit gas from said manifold to said ringto cool and clean said ring and said brushes.

5. The invention as defined in claim 1 wherein said housing is aconventional seal housing and wherein said brush assemblies occupy oneend of said housing, the other end of said housing being occupied by aset of shaft seals.

6. The invention as defined in claim 1 wherein said means for deflectingsaid leaf spring is a source of pressurized gas admitted to saidhousing.

7. The invention as defined in claim 1 wherein the center of said leafspring is normally driven against said inner wall to a positive stop.

mg?" UNITED STA'IES PATENT omen CERTIFICATE OF CORRECTION Patent No.3,826,942 Dated July 30, 1974 lnven tofls) John J. Twarog, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

' Column 1, li ne 11, "6,5000" should read 6,500

Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. 0. MARSHALL DANN V Attesting Officer Commissioner ofPatents .J

mg? v UNITED S'IA'IES PATENT ormcm CERTIFICATE OF CORRECTION Ratent No.3,826,942 Dated July 30, 1974 Invcotofls) John J. Twarog, Jr.

It is certified that error appears in the above-identified patent endthat said Letters Patent are hereby corrected as shown below:

- Column 1, li e 11, "6,5000" should read 6,500

Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. I C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. A slip ring assembly for providing an electrical connection to aconductive ring fixedly mounted on the periphery of a rotating shaft,the combination comprising: a stationary annular housing having axiallyspaced end walls and outer and inner peripheral walls, said housingbeing coaxial with said shaft, said inner wall surrounding saidconductive ring and being spaced therefrom, and having a plurality ofcircumferentially spaced openings; a plurality of radially displaceablecircumferentially extending leaf springs supported within said housing;first and second electrically conductive contact brushes mounted on therespective ends of said leaf springs; and means for radially drivingsaid leaf spring toward said axis to drive each of said brushes throughsaid openings and into contact with said ring.
 2. The invention asdefined in claim 1 and a support for each of said leaf springs, saidsupport comprising a plurality of relatively heavy support springsextending circumferentially within said housing, the ends of saidsupport springs being fixed, the spaces between said support springs andthe outer peripheral wall of said housing defining a chamber, the centerof said support spring being connected to the center of said leafspring, said support spring being radially inwardly deflectable todeflect said leaf spring and drive said brushes into contact with saidring.
 3. The invention as defined in claim 2 wherein said means fordeflecting said leaf spring comprises means for admitting gas underpressure to said chamber for radially deflecting said support spring. 4.The invention as defined in claim 3 and a plurality of gas inletmanifolds in said housing, the ends of said support springs being fixedagainst said manifolds, and gas passageways through said manifold andsaid inner peripheral wall to admit gas from said manifold to said ringto cool and clean said ring and said brushes.
 5. The invention asdefined in claim 1 wherein said housing is a conventional seal housingand wherein said brush assemblies occupy one end of said housing, theother end of said housing being occupied by a set of shaft seals.
 6. Theinvention as defined in claim 1 wherein said means for deflecting saidleaf spring is a source of pressurized gas admitted to said housing. 7.The invention as defined in claim 1 wherein the center of said leafspring is normally driven against said inner wall to a positive stop.